Why ammonium hydroxide precipitates metal salts?

When I was going through the chapter on pnicotgens, I got to know that ammonia acts as a Lewis base and it dissociates in water giving out hydroxide ion and the further hydroxide of ammonia, which we refer to as ammonium hydroxide, precipitates metal salts in a form of metal hydroxides.

I want to know the reason why this thing happens. According to me, ammonium hydroxide should form a complex with the metal being a base after donating a pair of electrons. Correct me if I am wrong. A reaction is given below as an example of a reaction between ammonium hydroxide and zinc sulfate:

$$\ce{ZnSO4 + 2 (NH3 * H2O) → Zn(OH)2 + (NH4)2SO4}$$

• Unfortunately, solubility is nowhere near that simple. – Zhe Feb 13 '19 at 14:25
• Zinc forms ammine complex $\ce{[Zn(NH3)4]^2+}$ all right in liquid ammonia and when exposed to ammonia gas. It just so happens that in aqueous solution zincate $\ce{[Zn(OH)4]^2−}$ formation is favored. – andselisk Feb 13 '19 at 14:28
• Not so much $\ce{Zn(OH)_4^{2-}}$ as precipitated $\ce{Zn(OH)_2(s)}$. Getting the hydroxy-complex anion in large amounts requires a stronger basic solution than that formed by ammonia in water. – Oscar Lanzi Feb 14 '19 at 14:55
• Not sure what you are looking for. Ammonia is a ligand that can help solubilize metal ions. Exactly when that happens or doesn't happen isn't that easy to predict from first principles. In this case, you have several equilibria in play which further complicates the situation. – Zhe Feb 15 '19 at 13:03
• I just want to know that why Ammonium hydroxide precipitate out the metal salt what's the reason behind that because in some metals Ammonia form complexes whereas in others it precipitate them out why this difference arises is it due to the configuration of different metals I mean is it due to the different nature of metals or something else thanks in advance. – David Wax Feb 15 '19 at 13:16